With its allure of free energy and maintenance-free operation for lifetimes of 10 and even 15 years, energy harvesting (EH) is grabbing the attention of potential users in many markets. Recent EH developments have made great progress, and the pieces appear to be falling into place.

System components such as microcontrollers (MCUs), RFICs, and power-supply ICs have had to drastically reduce their power consumption and increase performance to complete a useful energy-harvesting system. In addition, software that controls the power management, data collection, and transmission processes while avoiding any unnecessary power consumption is essential.

A joint article by Powercast (Harry Ostaffe, Charlie Greene) and AVX (Bharat Rawal), titled “Power Module and Double Layer Capacitor Harvest Energy From Radio Signals“ was recently published in Power Electronics Technology. Combining Powercast’s P2110 Powerharvester receiver with an AVX Double-Layer Capacitor (super-capacitor) results in a battery-free, wireless power supply that can be used for low power applications such as wireless sensors. The article describes in detail the operation of the P2110 Powerharvester.

Figure 1 shows a general block diagram of the P2110 Powerharvester. The RF energy is converted to DC and stored into an external capacitor. For some applications a small electrolytic capacitor may be sufficient, but other cases will require more energy and therefore a larger double-layer capacitor (super-capacitor). The voltage on the external capacitor is typically managed between the operating range of 1.25V, when the output voltage is turned on, and turned off at the low threshold of 1.05V. The boost converted is used to provide a regulated output voltage from a range of 2-5.25V to accommodate a wide range of applications.

The timing diagram in Figure 2 provides more detail on the operation. The INT pin provides a logic-level output to indicate when Vout is active, and the RESET pin enables an external device such as a microtontroller or external timer to turn off Vout. The RESET function saves energy and allows the P2110 to recharge the capacitor more quickly.

Figure 3 show a system-level implementation that is typical in a wireless sensor, such as HVAC control sensors using ZigBee, WiFi, or other protocols, or industrial sensors using ISA100 or WirelessHART.